In the field of the magnetic disc, a 2 MB MF-2HD flexible disc using Co-modified iron oxide has been generally loaded in a personal computer. However, along with the rapid increase in the amount of data to be dealt with, the capacity of the disc has become insufficient and the increase of the capacity of the flexible disc has been demanded.
In the field of the magnetic tape also, along with the prevalence of the office computer, such as minicomputers, personal computers and work stations, magnetic tapes for recording computer data as external storage media (so-called backup tapes) have been eagerly studied. For putting magnetic tapes for such usage to practical use, the improvement of recording capacity has been strongly demanded for achieving high capacity recording and the miniaturization, in particular, conjointly with the miniaturization of a computer and the increase of information processing performance (i.e., the increase of throughput).
Magnetic recording media comprising a nonmagnetic support having coated thereon a magnetic layer comprising an iron oxide, a Co-modified iron oxide, CrO2, ferromagnetic metal powder (MP), or hexagonal ferrite powder dispersed in a binder have been conventionally widely used. Of these powders, ferromagnetic metal fine powders and hexagonal ferrite fine powders are known to be excellent in high density recording characteristics. In the case of a disc, as high capacity discs using ferromagnetic metal fine powders which are excellent in high density recording characteristics, there are 10 MB MF-2TD and 21 MB MF-2SD, and as high capacity discs using hexagonal ferrite, there are 4 MB MF-2ED and 21 MB Floptical, however, any of these are not satisfactory with respect to capacities and performances. As is the circumstance, various attempts have been made to improve high density recording characteristics. For example, high capacity and high density recording of from 100 M to 120 M, e.g., LS-120 and ZIP, has been realized, and now even higher density recording of areal recording density of 0.2 G bit/inch2 or more has been demanded. In addition, due to the requirement for shortening access time, the speed of rotation of discs has a tendency to increase.
In these high density and high rotation or high transfer magnetic recording media, further higher capacity has been required and supports are required to be thinner.
When a support becomes thinner, pinholes which were not generated before come to occur. In particular, in a polyamide support, the generation of a pinhole having a diameter of 30 μm or larger is confirmed. A coating solution leaks through a pinhole at the time of coating and transfers to a web, which leads to the generation of dropout (DO).
For compensating for this drawback, measures such as preventing spattering of a coating solution and detecting the soiled position have been taken, however, the drawback could not be compensated for with certainty.
As a means for preventing the generation of pinholes, it has been conventionally performed to coat a radiation-curable resin on a support as a subbing layer, but a subbing layer must be coated thickly to prevent pinholes. As a result, new problems have arisen such that not only high capacity cannot be achieved but also head touch worsens and the S/N ratio lowers.